Promise#done

/**
* Handle the ultimate fulfillment value or rejection reason, and assume
* responsibility for all errors. If an error propagates out of result
* or handleFatalError, it will be rethrown to the host, resulting in a
* loud stack track on most platforms and a crash on some.
* @param {function?} onResult
* @param {function?} onError
* @returns {undefined}
*/